1. Field of the Invention
The present invention relates to a power supply circuit, and more particularly to an electrotheological fluid damping control system which is comprised of a vibration damping apparatus and a high voltage power supply circuit which is electrically connected to a capacitive load of an electrode section of the vibration damping apparatus or an electrode of a power transmission apparatus using electrorheological fluid so as to apply a desired voltage to the capacitive load, and which is used to cut off the voltage applied to the capacitive load and to vary, continuously or in steps, the voltage applied to the capacitive load, to produce high-speed response of the power supply circuit when the supply of the voltage to the capacitive load is cut off.
2. Description of the Related Art
There has heretofore been known electrorheological fluid type applied equipment, such as a vibration damping apparatus or a power transmission apparatus, of a type wherein the electrorheological fluid is interposed between electrodes and the viscosity of the electrorheological fluid to which a desired voltage is applied is used. A power supply circuit comprising a transformer and a rectifier circuit, which is electrically connected to the secondary winding of the transformer and provided with capacitors, is a power supply circuit suitable for use with this type of equipment. It is found that the response (a time interval from the time at which a desired voltage is applied to the time at which the orientation of molecules is completed and the viscosity of the molecules becomes constant) of the electrorheological fluid is several msecs. In order to make the most use of this response characteristic, it is necessary to set the response of the power supply circuit to high-speed response of a few msecs or less, preferably 500 .mu. sec or less. The power supply circuit should take into consideration the response at the time of application of a desired voltage to a load, i.e., a period from the time at which the primary side of the power supply circuit starts to supply power to the time at which the voltage on the secondary side of the power supply circuit fully increases to a voltage near a set voltage (i.e., increases to 90% of the set voltage). The power supply circuit should also take into consideration the response at the time of a voltage cut-off, i.e., a period from the time at which the primary side of the power supply circuit stops supplying power to the time at which the voltage on the secondary side of the power supply circuit sufficiently drops (i.e., decreases to 10% of the set voltage).
As a method of improving the response of the conventional power supply circuit, there is known one of increasing the ability to supply power from the primary side of the power supply circuit to improve the response of the power supply circuit at the time of the voltage application. The response of the power supply circuit may be several times the oscillating cycle or period. Thus, a sufficient response of the power supply circuit can be expected even if a generally-used oscillating frequency (oscillating period: 50 .mu. sec) of 20 KHz is used.
On the other hand, as methods of improving the response of the power supply circuit at the time of the voltage cut-off, there have been known a method of mounting a dummy load or resistor for discharging electric charges stored in capacitors of a rectifier circuit on the output terminal of the rectifier circuit, a method of reducing the capacitance of all of the capacitors in a rectifier circuit, a method of reducing the discharge time constant, and a method of increasing the magnitude of an alternating current oscillating frequency which is input to the primary winding of a transformer and reducing the absolute time constant while the same discharge time constant is being set to each oscillating period.
The method using the dummy resistor has a drawback in that since power is consumed by the dummy resistor, the entire operational efficiency is reduced and the quantity of heat generated increases. According to the method of reducing the capacitance of each capacitor, ripple on the output from the rectifier circuit increases, thus providing unstable output. The method of increasing the magnitude of the frequency of the input voltage has a drawback in that the design of the power supply circuit is difficult and elements to be used are also required to have high-speed response characteristics, thereby raising the manufacturing cost.